In recent years, a model incorporating a camera module in a cellular phone body has been used in the majority of cellular phones. Such camera modules need to be accommodated in housings of cellular phones and are accordingly required to have their size and weight reduced more than in the case of digital cameras.
There are an extremely large number of examples in which, among such camera modules, a camera module whose lens-driving device serves an autofocus function is installed in an electronic device such as a cellular phone. Lens-driving devices are divided into various types: a stepping motor use type, a piezoelectric element use type, and VCM (Voice Coil Motor) use type and are in the marketplace.
Camera modules with an autofocus (AF) function, as described above, are taken for granted, and in this circumstance, there are recently some suggestions to further improve the autofocus function. According to one of the suggestions, feedback control actuates the autofocus.
A focus control circuit used in a camera module that performs an autofocus action while implementing feedback control is disclosed in PTL 1. According to PTL 1, the output signals of a position-detecting element for detecting the position of a lens are used to implement feedback control on the basis of a difference from a target position of the lens that is set from the outside, and the accuracy of focus can be improved.
Achieving the autofocus action requires a lens-driving device. The lens is typically supported in some way so as to be movable. The movable range of the lens is limited, and there is a member (stopper) for limiting the movable range. Accordingly, there is a problem in that a collision of a movable portion including the lens with the stopper makes a collision noise. An example of a method for reducing the collision noise is disclosed in PTL 2. According to PTL 2, an elastic body is used as a member serving as the stopper to reduce the collision noise. Another method for reducing the collision noise is disclosed in PTL 3. According to PTL 3, the range in which a lens unit is movable is divided into the predetermined number of divided ranges, and the collision noise is reduced in a manner in which the lens unit is caused to move a unit movement amount with a waiting time for suppression of vibration set. PTL 2 discloses a mechanical countermeasure, and PTL 3 discloses a countermeasure relating to an aspect of control.